"Hospital Playlist" is a popular South Korean television series that revolves around five doctors who have been friends since they entered medical school in 1999. Here are the roles and responsibilities of the main characters in the series:

1. Lee Ik-jun (played by Jo Jung-suk): He is an Associate Professor in the Department of General Surgery. His responsibilities include performing surgeries, diagnosing patients, and providing treatment for diseases and injuries of the digestive tract, abdomen, and other major parts of the human body.

2. Ahn Jeong-won (played by Yoo Yeon-seok): He is an Assistant Professor in the Department of Pediatric Surgery. His role involves diagnosing and treating health issues specific to infants, children, and teenagers. He performs surgeries on younger patients and provides them with post-surgery care.

3. Kim Jun-wan (played by Jung Kyung-ho): He is an Associate Professor in the Department of Cardiothoracic Surgery. His role is to perform surgeries on the organs inside the thorax (the chest), generally treatment of conditions of the heart and lungs.

4. Yang Seok-hyeong (played by Kim Dae-myung): He is an Assistant Professor in the Department of Obstetrics and Gynecology. His responsibilities include providing medical care related to pregnancy, childbirth, and the female reproductive system. He also performs surgeries related to his field.

5. Chae Song-hwa (played by Jeon Mi-do): She is an Associate Professor in the Department of Neurosurgery. Her role involves performing surgeries on the brain, spinal cord, and peripheral nerves to treat conditions such as brain tumors, neurological disorders, and injuries.

All these doctors also have additional responsibilities such as teaching medical students, conducting medical research, and participating in hospital administration.